This invention relates generally to a system which can automatically stop, start and/or proportionally regulate the flow of relatively dry, flowable, particulate or pulverulent material, such as detergent, which is to be admixed with a liquid to form a liquid cleaner. When the system of the invention is used in conjunction with electrical and pneumatic controls, the detergent can be automatically mixed with water to a particular consistency, and this consistency can be efficiently reproduced as desired. The system is particularly designed for self-service or automatic car washes.